Relation Between Electromagnetic Wave Intensities And Amplitudes

The intensity of an electromagnetic wave is the power per unit area.  For intensity I, speed of light c, and average energy density <u>:

I = c<u>

The electric and magnetic energy densities of electromagnetic waves are equal, and, the electromagnetic wave amplitudes are related by the speed of light.  Therefore, for maximum energy density uₘ, electric field amplitude Eₘ, magnetic field amplitude Bₘ, electric constant εₒ and magnetic constant  μₒ:

uₘ = εₒEₘ² / 2 + Bₘ² / (2μₒ) = εₒEₘ² = Bₘ² / μₒ 

Since <u> = uₘ / 2:

I = cεₒEₘ² / 2 = cBₘ² / (2μₒ)